package com.jiaobuchong.demo.first;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import java.io.IOException;
import java.util.StringTokenizer;

public class WordCount {

    //继承mapper接口，设置map的输入类型为<Object,Text> 输入键类型为Object 输出键为文本
    //输出类型为<Text,IntWritable>
    public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable> {
        //one表示单词出现一次
        private final static IntWritable one = new IntWritable(1);
        //word存储切下的单词
        private Text word = new Text();

        // 把输入的值拆分为键值对
        public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
            //对输入的行切词
//            map方法的前两个参数分别为输入的键和值，通过下面的代码先将text格式的字段转为java的String类型
            StringTokenizer itr = new StringTokenizer(value.toString());
            while (itr.hasMoreTokens()) {
                //切下的单词存入word
                word.set(itr.nextToken());
//                使用context的write方法将数据进行记录
                context.write(word, one);
            }
        }
    }

    //继承reducer接口，设置reduce的输入类型<Text,IntWritable>
    //输出类型为<Text,IntWritable>
//    Reducer类是一个泛型类，四个参数分别表示输入键，输入值，输出键，输出值
    public static class IntSumReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
        private IntWritable result = new IntWritable();

        // 把输入的数据拆分为键值对
        public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
            int sum = 0;
            //对获取的<key,value-list>计算value的和
            for (IntWritable val : values) {
                sum += val.get();
            }
            //将频数设置到result
            result.set(sum);
            //收集结果
            context.write(key, result);
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf, "word count");
        job.setJarByClass(WordCount.class);
        job.setMapperClass(TokenizerMapper.class);
        job.setCombinerClass(IntSumReducer.class);
        job.setReducerClass(IntSumReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }

}
